To exhibit an assist function even for various types of commercially available screwdrivers.

A screwdriver rotation assist adapter includes: a grip portion 1 in contact with a palm; a shaft 2 rotatably installed to the grip portion 1; a finger catching portion 100 fixed to the shaft 2; a base 7 fixed to the shaft 2 and provided with two surfaces parallel to the shaft 2 and at least opposite to each other, and in addition, provided with bolt holes 71 in the two surfaces; two pressing plates 9 each having a shape coming into contact with each of two surfaces of the base 7, and having a through-hole 91 in correspondence with the bolt hole 71; and two bolts 8 each screwed into the bolt hole 71 of the base 7 through the through-hole 91 of each of the two pressing plates 9.